With their receiving corps thinned even further by injury, the Giants are making one thing very clear — Rueben Randle needs to work harder and be smarter.

The second-round pick from LSU remained under the microscope yesterday after Big Blue revealed wideout Ramses Barden had suffered a concussion in the waning moments of Sunday’s loss to the Eagles, a development that only added to the Giants’ woes at that position.

Hakeem Nicks has missed the past two games with knee swelling that apparently isn’t getting better, so Barden’s injury means two of the Giants’ top four receivers could be unavailable when they play host to the 0-4 Browns on Sunday.

The Giants expect Randle to help fill that void after confirming questions about his work ethic and grasp of the offense that first surfaced publicly when NBC analyst Cris Collinsworth mentioned them during the broadcast of the Philadelphia game.

Tom Coughlin downplayed Collinsworth’s comments, but Eli Manning and other Giants — and even Randle himself — admitted there is concern within the organization about how the 6-foot-4, 210-pound rookie is struggling to keep up.

Randle has just one catch for four yards during the Giants’ 2-2 start, prompting Manning — who rarely criticizes teammates to the media — to raise some eyebrows yesterday by saying Randle still needs to adjust to the intensity of pregame preparation in the NFL.

“Rueben’s just young and trying to figure out what it takes to compete and get mentally and physically ready for upcoming games,” Manning said. “He has talent. He’s been working better and has an understanding of just how we work and how we prepare each week.

“He’s going to have to play for us, whether it’s this week or sometime, and I believe he can do that. He can help us out.”

Questions about Randle’s intensity were one of the reasons such an impressive physical specimen from a team that played in the BCS championship game last year fell all the way to the bottom of the second round, so the current issues aren’t exactly a surprise.

Randle’s biggest problem is thinking on his feet. The Giants give their receivers several routes for each pass play, and they’re supposed to pick the route best suited to attack the coverage they see at the line of scrimmage. Randle has been failing at this, which explains his inability to get on the field despite a barrage of injuries to the Giants’ receivers.

As a result, Randle’s coaches and teammates continue to implore him to “play faster.”

“They want me to go into the game knowing what the defense is going to do,” Randle said yesterday. “Gaining the coaches’ trust is going to be the main thing. The offense we have here is complex, and you have different routes on different coverages. You just have to pick up on things like that.”

Randle said he first learned of Collinsworth’s dig via Twitter, but claims it doesn’t bother him.

“I’m not concerned because I know what’s going on inside the building — which is all that matters,” he said.

Randle isn’t a personal project of Manning’s just yet, but the Giants star said he is trying to help the rookie come around.

“We talk and go over things to try to get on the same page,” Manning sad. “He is young, and it takes time for a quarterback and a receiver to gain that trust and confidence and get on the exact same page and be able to understand what the other is expecting. The more reps he gets in practice, the better we’ll get.”

Giants wideout Victor Cruz certainly hopes so.

“[Receivers] are dropping like flies, man,” Cruz said. “Every time I look up there’s another one gone.”